Sideboard



FIG. 1 is a left front top perspective view of a sideboard showing my new design;

FIG. 2 is a side view, the opposite side being a mirror image thereof;

FIG. 3 is a front elevational view thereof; and,

FIG. 4 is a top view thereof.

The bottom and rear elevational views of the design are not shown and form no part of the claimed design. The dashed lines represent environmental elements only and form no part of the claimed design. 

The ornamental design for a sideboard, as shown and described. 